1. Field of the Invention
This invention relates to a heating and shaping system using microwave focused beam heating, and more particularly, in one non-limiting embodiment of the invention, to a glass pilot line having a furnace having two heating chambers, wherein the first heating chamber is used to preheat one or more glass substrates to a first temperature; the second heating chamber maintains the substrates at the first temperature and heats and shapes selected portions of the one or more glass substrates using microwave focused beam heating, and the first heating chamber is used to controllably cool the one or more glass substrates to anneal or thermally temper the one or more shaped glass substrates.
2. Discussion of the Presently Available Technology
Bending devices, commonly referred to in the bending art as bending irons or shaping irons, are well known in the art for shaping one or more glass sheets for use in the manufacture of monolithic and laminated transparencies for land, water, air and space vehicles. The method for shaping the glass substrates or sheets for use in the manufacture of transparencies for land and water vehicles usually includes providing one or more glass sheets having seamed or smoothed edges and a predetermined size; moving the glass sheets supported on a bending iron through a furnace to heat soften the glass sheets; shaping the glass sheets; controllably cooling the shaped glass sheets to anneal or thermally temper the shaped glass sheets, and using the shaped glass sheets in the manufacture of a transparency for a land or water vehicle. The method for shaping glass substrates or sheets for use in the manufacture of transparencies for air and space vehicles usually includes providing one or more glass sheets having seamed or smoothed edges and a predetermined size; moving the glass sheets supported on a bending iron through a furnace to heat soften the glass sheets; shaping the glass sheets; controllably cooling the shaped glass sheets to anneal the shaped glass sheets; cutting the shaped glass sheets to a second predetermined size; seaming or smoothing the edges of the shaped glass sheets; chemically tempering the shaped glass sheets, or thermally tempering the shaped glass sheets, and using the tempered shaped glass sheets in the manufacture of a transparency for an air or space vehicle.
The difference of interest in the present discussion between shaping glass sheets for use with transparencies for land and water vehicles and shaping glass sheets for use with transparencies for air and space vehicles is that the glass sheets for use with transparencies for land and water vehicles are cut to size before shaping or bending, whereas glass sheets for use with transparencies for air and space vehicles are cut to an over size before shaping and cut to size after bending. For purposes of clarity, the process presently available for shaping glass sheets for use with transparencies for land and water vehicles is also referred to herein as “cut-to-size process”, and the process presently available for shaping a glass sheet for use with transparencies in air and space vehicles is also referred to herein as “cut-after-bend process”.
The cut-to-size process can be used for making transparencies for land and water vehicles because the glass sheets are thinner, e.g. a single glass sheet for making transparencies for land and water vehicles has a thickness in the range of 1.80 to 2.00 millimeters (“mm”), and usually two sheets have a thickness of 3.60 to 4.00 mm. The thickness of the glass sheets for making transparencies for air and space vehicles, on the other hand, are thicker e.g. a single glass sheet for making transparencies for air and space vehicles has a thickness in the range of 1.80 to 19.00 millimeters (“mm”), and usually two sheets have a thickness of 3.60 to 12.00 mm. or three sheets have a thickness of 5.40 to 18 mm. Because the stack of glass sheets used for making transparencies for air and space vehicles are thicker, the glass sheets remain in the furnace on the bending iron for a longer period of time to heat the stack of sheets to their shaping or bending temperature. Maintaining the glass sheets for long periods of time on a heated bending iron usually results in marring surface areas of the glass sheet in contact with the bending iron. The marring of the glass sheet can cause distortions on the surface of the glass sheet, which can make the optical quality of the glass sheet and subsequently formed transparency unacceptable.
One solution to the problem is to provide a bending iron that has improvements in its design to prevent the marring of the surface of the glass sheet in contact with the bending iron. Such a bending iron is disclosed in USPA '494. Another solution to the problem is to reduce the temperature of the furnace and/or the time period of the heating cycle for shaping the glass sheets to reduce or eliminate marring of the surface of the glass sheet in contact with the bending iron during the sheet shaping process.
As can now be appreciated by those skilled in the art, it would be advantageous to provide a process of, and equipment for, shaping glass sheets for use in aircraft and space transparencies using the cut-to-size process, while eliminating marring of the surface of the glass sheet in contact with the bending iron.